The embodiments disclosed herein generally relate to coated substrates, efficient application of coating compositions, and systems and methods for analyzing the quality of coating compositions.
Xerographic toners contain thermoplastic resins that are selected in part to ensure adhesion to media in a two roll fusing nip. Fusing takes place at a specified temperature, pressure and dwell time. The fusing conditions may not be consistent with quality standards for image permanence and durability in commercial printing markets. For this reason clear, protective overcoats may be applied over the print using some form of liquid film coating process followed by suitable drying and/or curing. To the extent that the surface of the xerographic print at the time of coating contains residual low surface tension fuser release oil, liquid film coatings will experience a range of surface tension defects known to the industry. One type of defect, referred to as “pin holes,” is caused by the presence of oil on the substrate. The oil prevents complete wetting of the substrate by to coating composition. Another kind of defect, referred to as haze, occurs when a coating composition surrounds droplets of oil, resulting in a two phase mixture that is not optically transparent.
In the past, quality problems associated with surface tension defects have been overcome by incorporating a process delay before application of the coating, thereby allowing residual fuser oil to diffuse below the surface. The delay required to overcome surface tension defects in this manner is typically 30 minutes to several hours after fusing. From a process perspective, the delay time necessitates two separate operations—1) production of the fused image and 2) application of the image overcoat. It is required to have a time delay between the two operations because the requisite delay time cannot be accommodated in-line at process speeds of existing Xerographic engines.
It would be useful to develop a more efficient method and system for producing the fused image and applying a protective coating.